When it comes to what’s under the hood, the 2012 Mercedes-Benz CLS63 AMG launches with a name that is now more misleading than ever. AMG’s “63” moniker, after all, never was entirely correct: At 6208 cc, the last-gen CLS63’s naturally aspirated M156 engine missed the 6.3-liter mark by less than a 10th of a liter. And now, most AMG “63” cars are having their 6.2 replaced by a twin-turbocharged 5.5-liter V-8 dubbed M157.

The smaller, turbocharged engine manages far better fuel economy than its predecessor (Mercedes expects EPA ratings for the 2012 CLS63 to be 16 mpg in the city and 21 on the highway, up from 12/18 for its predecessor) with, conveniently, more power. This CLS63 chalks up an 11-hp increase over the old car, from 507 to 518. Torque, meanwhile, gets a kick upward of 51 lb-ft, from 465 to 516. If that’s not enough, the optional Performance package cranks boost from 14.5 psi to 18.8, ratcheting power up to 550 horses and torque to 590 lb-ft.

CLS: Charges like a Supercar

Aided by a seven-speed automatic—the same transmission found in other V-8 AMG cars, it has a multiplate wet clutch replacing the torque converter—the CLS63 charges forward like a supercar and pulls relentlessly way beyond the 100-mph barrier. Top speed is governed at 155 mph, or 186 with the Performance pack, which also drops Mercedes’ estimated 0-to-60-mph time from 4.4 seconds to 4.3. As we clocked a previous-generation CLS63 to 60 in 4.1 seconds, we’ll call those estimates conservative. Turbocharging does squelch some of the bawdy V-8 roar that contributes so much to our enjoyment of the M156, but we’d say the extra power and torque are an adequate salve for that disappointment.

The AMG brand is often associated with straight-line performance more than balanced cornering. For some vehicles in its vast portfolio, which includes literal heavyweights such as the S-class and G-wagen, that is accurate; but the CLS defies that stereotype. The steering—controlled by a fat, somewhat oversized, Alcantara-wrapped wheel—is a touch too light but very precise, and the adjustable suspension allows only minimal body roll, behaving predictably up to the limits of adhesion. Try to surpass those limits, and the traction-control system intervenes sharply. It can be turned off entirely, but doing so is only recommended for trained professionals. The brakes feel a bit too aggressive around town but are perfect on the open road.

Civil Pretender

If you drive the CLS63 AMG with civility (good luck with that), it is actually quite comfortable. And it’s even green (sort of): The engine automatically shuts off when the car is stationary, and a prominent “eco” light illuminates in the instrument cluster whenever the driver isn’t sucking too much fuel. Okay, so that’s not really green at all. Any effort at political correctness is thoroughly negated by AMG’s design team. The grille, with its single horizontal crossbar, quotes Mercedes’ traditional sporty motif like the grille on the gullwing SLS does. From the gigantic front air intakes, venomous-looking LED headlights, and wide fenders to the quadruple exhaust tips, the CLS63 AMG is a hostile take on the already extroverted second-generation CLS, and it has us in equal parts scared and seduced.

With the new CLS AMG’s attitude and performance, Mercedes’ continued use of the 63 moniker is fine with us. Memo to the industry: This is what engine downsizing should be.

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Whenever you add the letters “AMG” to a Mercedes model, you are sure to get breathtaking performance, and the CLS63 AMG is no exception.